JP6718622B2 - Gap sensor and gap measuring method - Google Patents

Description

The present invention relates to a gap sensor for detecting a gap between opposed member surfaces, more specifically, a gap distributed in a plane, and a measuring method thereof.

In the assembly technology of ships, aircrafts, etc., when assembling an external panel and an internal part, relative position alignment is required. For example, the main wing of an aircraft has a box structure including a frame made of girders and ribs, and its base end has a frame structure for connecting to a fuselage. A fixing portion (bracket) having a substantially cylindrical structure that receives the base end portion of the main wing is formed on the body, and the base end portion of the main wing is inserted into the fixing portion and coupled in a structure such as a tea canister. The fixing portion of the fuselage is configured such that the plate member that constitutes the base end portion of the main wing is sandwiched between two plate members, and both sides of the plate member at the base end portion have a gap of about several mm from the plate member of the fixing portion. Are facing through. Each plate member is a conductive material such as aluminum alloy or carbon fiber. In the joining work, alignment adjustment is performed so that the body and the main wing have a predetermined positional relationship, and then a spacer matching the shape of the clearance space is inserted and fastened. The same applies to the case where the body is divided into a front body, a middle body, and a rear body and then manufactured, and then the body parts are joined to form the body.

Japanese Patent No. 4832512 JP, 2005-79979, A

By the way, the gap at the joint position defined by the plate member of the main wing substrate part after alignment and the plate member of the fuselage fixing part is measured at multiple points by a gap sensor (feeler gauge, thickness gauge), and the three-dimensional shape of the gap space is measured. The shape of the spacer is specified by acquiring the data.

In an electronic gap sensor using a capacitance sensor, a probe portion is usually formed in an elongated shape, and a flat detection electrode is arranged on the tip side thereof. When the electrodes are arranged on both surfaces of the probe, it is necessary to sandwich both sides of each electrode layer with guard patterns, so that six conductive layers are required as a whole, and there is a limit to making the probe thin. In recent years, in press die processing of plate materials for ships, aircrafts, automobiles, etc., even when adjusting the clearance between a die and a punch, three-dimensional measurement of the clearance is necessary, and measurement of smaller clearance is required. ..

Further, since the wheels can be attached with the main wing and the fuselage being coupled, it is necessary to perform the clearance measurement quickly and accurately in order to enable movement by the wheels. Further, in press die processing of plate materials for ships, aircrafts, automobiles, etc., there is a similar problem because three-dimensional measurement of the clearance space is necessary even when adjusting the clearance between the die and the punch.

In an electronic gap sensor using a capacitance sensor, generally, a predetermined signal such as a rectangular wave is applied to the electrodes, and the electrode pattern is actively guarded through a buffer. That is, as illustrated in FIG. 1A, the probe includes a detection electrode De′ to which a probe signal is applied and guard patterns G1 and G2 that make the periphery and the back surface of the electrode have the same potential as the electrode. A probe signal is applied to the electrode patterns E1 and E2 including the electrode De', and a current corresponding to the electric capacitance of the measurement target is detected. Further, the detected potential of the electrode De' is actively guarded to the guard patterns G1 and G2 at the electrode potential via the buffer so that the periphery of the electrode is kept at the same potential. The active guard can suppress the electric field other than the electric field generated between the electrode and the measurement target to improve the accuracy of the capacitance measurement.

However, since the potential of the electrode De' during measurement is set to the guard potential of the guard pattern G1 or G2, it is not possible to simultaneously measure a plurality of electrodes surrounded by the same guard pattern. This is because each electrode signal is different and the corresponding guard signal is different for each electrode.

The present invention has been made in view of such a problem, and according to the present invention, it is possible to provide an electronic gap sensor and a gap measuring method for obtaining gap data with small measurement error and high reproducibility.

According to a technical aspect of the present invention, a gap sensor for detecting a gap between a surface of a first member having conductivity and a surface of a second member having conductivity, which face each other, by a capacitance measuring method, A probe extending along the main axis direction and a main body, wherein the probe has a proximal end connected to the main body and a plurality of electrodes provided on the distal end side; and the probe has a first conductive layer, a second conductive layer, The first conductive layer defines a first surface of the probe, a first electrode group is formed in an array, and is electrically connected to the first electrode group. A first guard layer that is not connected to the first conductive layer is formed, the third conductive layer defines a second surface of the probe, and a second electrode group is formed at a position corresponding to the first electrode group. A second guard layer electrically disconnected from the second electrode group is formed, the second conductive layer is disposed between the first conductive layer and the third conductive layer, and the first electrode group and the second electrode are formed. A guard electrode is formed at a position corresponding to the group, and a signal line pattern that is not electrically connected to the guard electrode is formed. The signal line pattern is electrically connected to each electrode of the first electrode group and the second electrode group. To be done. Furthermore, the control unit of the main body applies a search signal to the first guard layer, the guard electrode, and the second guard layer, and connects each electrode of the first electrode group and the second electrode group via the signal line pattern. Voltage is clamped by the search signal and the clamp current by the voltage clamp is detected to measure the gap at each electrode position.

According to another technical aspect of the present invention, a gap measurement for detecting a gap between a surface of a conductive first member and a surface of a conductive second member facing each other by a capacitance measuring method. The method includes forming a plurality of electrode pairs and guard layers at corresponding positions on both surfaces of the probe, generating a probe signal, applying the probe signal to the guard layer, and each of the plurality of electrode pairs. The electrodes are independently voltage-clamped to the probe signal, the capacitance at each electrode position is detected by measuring the clamp current of each electrode, and each electrode position is based on the capacitance. And measuring the gap at.

(A) is a conceptual diagram of the conductive layer of the electrode part concerning related technology, (b) is a conceptual diagram of the conductive layer of the electrode part concerning this invention. The top view which shows the clearance gap sensor of this embodiment. The conceptual diagram showing the cross-section of the probe electrode part of this embodiment. The conceptual diagram of a control part control circuit. The conceptual diagram which shows the principle of gap measurement by a gap sensor. A conceptual diagram of gap measurement by a gap sensor. The conceptual diagram which shows the probe electrode concerning other embodiment. The bottom view of the sensor body concerning other embodiments.

A preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows a top view of the gap sensor according to the present embodiment. The gap sensor 1 includes a probe 2 on which an electrode for detecting a gap is arranged, and a main body 21 connected to the probe 2 via a connector 20 as a probe supporting portion. The main body 21 includes a control unit 10 that applies a voltage to the detection electrode of the probe 2 and measures a displacement current. The probe 2 has an elongated shape extending in the main axis direction (Xc) in the XY plane, and is inserted into the gap space G formed between the surfaces S1 and S2 of the electrically conductive members such as the opposing workpieces to form a gap. To measure. The probe 2 also includes a flexible printed circuit board 5 provided with an electrode portion 3 including an electrode pair array 4. The flexible printed board (FPB) 5 has an elongated three-layer structure extending in the direction of the main axis X in FIG. 1, and has a space between the elliptical electrode 4 and the surfaces S1 and S2 of the conductive material to be measured. A response voltage is measured by applying a predetermined potential, and the gap at the electrode position is acquired based on the acquired capacitance. A filler film for attracting with a magnet is formed on the surface of the probe 2 including the electrode portion 3.

<Probe electrode>
A conceptual diagram of the configuration of the conductive surface of the electrode portion 3 of the probe 2 is shown in FIGS. The flexible printed circuit (FPC) 5 has a guard pattern G1 (first conductive layer C1) defining a front surface (first surface) P1 and a guard pattern G2 (third conductive layer C3) defining a back surface (second surface) P2. It has a signal pattern Es (second conductive layer C2) sandwiched between two guard patterns. The signal pattern Es is a group of electrode signal patterns Esi electrically connected to the electrodes Ei independently. Further, an insulating layer (not shown) is arranged between the conductive layers. In FIG. 1B, the electrode Ei has a circular shape for convenience, but may have an arbitrary shape such as an ellipse or an ellipse.

Referring to FIG. 3, in the electrode part 3, an electrode pattern E1 is formed on the first conductive layer C1, and a ring-shaped gap gp1 is formed as an insulator between the electrode pattern E1 and the guard pattern G1 formed so as to surround the periphery. Is not electrically connected. An electrode pattern E2 is formed on the third conductive layer C3, and a ring-shaped gap gp2 is formed between the electrode pattern E2 and the guard pattern G2 formed so as to surround the periphery thereof, and is not electrically connected. The electrode pattern E1 and the electrode pattern E2 are formed at the same position in the XY plane to form one electrode pair.

A guard pattern Ge is formed on the second conductive layer C2 at a position corresponding to the electrode pair, and is electrically connected to the guard patterns G1 and G2 via the via holes Gb1 and Gb2. On the other hand, the electrode pattern E1 is connected to the corresponding signal pattern Es1 of the second conductive layer C2 via the via hole Eb1, and the electrode pattern E2 is connected to the corresponding signal pattern Es2 via the via hole Eb2. A gap is formed between the via holes Eb1 and Eb2 and the guard pattern Ge in the second conductive layer C2. A plurality of electrode pairs are formed in the electrode portion 3, and each electrode Ei is connected to the corresponding voltage clamp amplifier VCAi via the signal pattern Esi.

The guard patterns G1, Ge, G2 are common to all the electrodes {Ei:i=1, 2...n} (n is the number of poles of the electrode 4). Therefore, since all the electrodes Ei are independently voltage-clamped to the same search signal Vp and the guard patterns G1, Ge, and G2 are simultaneously driven by the search signal Vp as described later, the entire electrodes are always at the same potential. ing. Since all the electrodes Ei and the guard pattern are electrically independent, they are in a virtual short-circuit state and are not actually short-circuited. Therefore, even with the three-layer structure, the capacitance can be measured with high accuracy. Furthermore, since each electrode Ei is independently voltage-clamped, it is also possible to simultaneously measure each clamp current and simultaneously obtain the electric capacitance. In the embodiment of FIG. 2, eight electrode pairs, that is, the number of electrodes n=16 will be described.

<Equipotential drive control>
FIG. 4 shows a conceptual diagram of the control circuit of the control unit 10. The control of the guard potential and the electrodes in the present invention adopts a unique equipotential driving method. The search signal generator SG generates a sine wave as the reference search signal Sp, the amplitude of which is controlled by the microcontroller MC. The search signal Sp is applied to the guard patterns G1, Ge, G2 as the guard signal Vp via the driver AMP.

The voltage clamp amplifiers (voltage clamp circuits) VCA1 to VCA16 are independently connected to the 16-pole electrodes E1 to E16 via signal patterns Es1 to Es16. Each voltage clamp amplifier VCAi receives the output Vp of the driver AMP as a search voltage and clamps the electrode Ei to the voltage Vp. Since the exploration voltage Vp is a sine wave, the voltage clamp amplifier VCAi is a variable voltage source.

The voltage clamp amplifier VCAi has a differential amplifier (op amp) as the main clamp amplifier OPia, and when the exploration voltage Vp is input to the non-inverting input terminal (+), the clamp output voltage Vfia connected to the inverting input terminal (−). The negative feedback control is performed so that the voltage is always equal to the search voltage Vp. Further, a resistor (clamp current detection resistor) Rsia for detecting the clamp current Isi is connected between the output terminal and the inverting input terminal of the main clamp amplifier OPia, and the electrode Ei is voltage clamped from the voltage across the resistor Rsia. It is possible to detect the clamp current (displacement current) when it is present.

The voltage ΔV across the resistor Rsia is amplified by the differential amplifier INA via the changeover switches SW1 and SW2, and the clamp current Iei=ΔV/Rsia can be detected.

The differential amplifier that constitutes the main clamp amplifier OPia has a slight input capacitance, bias current, etc., has temperature characteristics, and has characteristic variations. Since the capacitance to be probed is generally about pF or less, variations in the characteristics of the differential amplifier can cause a large measurement error. Therefore, a differential amplifier with uniform characteristics is adopted as the reference clamp amplifier OPib to compensate for error elements other than the search current.

More specifically, the voltage clamp amplifier VCAi has a reference clamp amplifier OPib as well as a make clamp amplifier OPia. The reference clamp amplifier OPib has the same external circuit as the make clamp amplifier OPia, and the search voltage Vp is input to the non-inverting input terminal (+) and the clamp output voltage Vf1b connected to the inverting input terminal (−) is always equal to Vp. Negative feedback control is performed so that It differs from the main clamp amplifier OPia only in that the clamp output voltage Vfib is not connected to the electrode Ei and has no load.

A resistor (reference current detection resistor) Rsib that detects a clamp current Iri under no load is connected between the output terminal and the inverting input terminal of the reference clamp amplifier OPib, and a voltage clamp is applied from the voltage across the resistor Rsib without load. It is possible to detect the reference clamp current Iri during the operation. The reference clamp current Iri reflects current components other than the current flowing through the electrode as a load. On the other hand, the clamp output voltages Vfia and Vfib of the two operational amplifiers are substantially equal to the search voltage Vp when the voltage is clamped. Therefore, the probe voltage Voia detected by the main clamp amplifier OPia can be interpreted as the net clamp current Isi flowing through the electrode Ei to which the bias current Iri derived from the differential amplifier is added. Therefore, the net clamp current Iei can be obtained by performing a differential operation on the output voltages Voia and Voib of the main clamp amplifier OPia and the reference clamp amplifier OPib.

The two differential amplifiers OPia and OPib forming the voltage clamp amplifier VCAi are preferably dual-type operational amplifiers in which operational amplifiers having uniform characteristics are contained in one package. Further, in order to protect the input of the differential amplifier, a resistor may be inserted between each non-inverting input terminal and the clamp output terminals Vfia and Vfib.

In the embodiment of FIG. 4, the electrodes Ei to be measured are sequentially selected by the changeover switches (analog switches) SW1 and SW2 under the control of the microcontroller MC, and the difference between the output voltages Voia and Voib is selected by the differential amplifier (instrumentation amplifier) INA. The clamp current is detected with high accuracy by performing dynamic calculation (current detection circuit).

Since the present invention employs a unique equipotential driving method in which each electric element is independently driven at the same potential, the clamp currents in a plurality of electrodes can be simultaneously measured in principle, but in the present embodiment, one difference is obtained. By combining the dynamic amplifier INA and the changeover switch, the capacitance of each electrode is measured in a time division manner. By using one processing system common to all the electrodes, stable processing is expected, and the main body 21 can be made compact. Further, in the present embodiment, the electrodes 4 of the probe 2 have 6 pairs and 12 poles, but it is possible to further increase the number of poles.
<Feedback control of adaptive search signal and charge clamp method>
Since the electrode Ei is a flat electrode and forms a virtual capacitor (capacitance C) between the electrode and the surface to be measured, the distance d between the electrode plates can be obtained by measuring the electrostatic capacitance as described later. ..

When a potential difference v occurs between the electrode Ei and the conductive surfaces S1 and S2, a charge q=±Cv is generated on each surface accordingly. When an alternating current is applied as a potential difference, a displacement current i=Cδv/δt flows through the electrodes. Since charges of opposite polarities appear in the same area as the electrodes on the conductive surface, there is a relationship of C=εS/d (ε is the permittivity of the gap space), where d is the distance between the electrodes and the conductive surface. Therefore, if the capacitance of the virtual capacitor is obtained from the measurement of the displacement current, the distance d=εS/C can be obtained. In the present embodiment, the potential difference v is controlled to exactly match the search signal Vp by using the voltage clamp as described above, and the search signal is expressed in the form of Vp(t)=Asin(2πft).

The clamp current with respect to the application of the exploration signal has a smaller amplitude and a lower detection accuracy as the electric capacitance C of the measurement target is smaller. Therefore, in the present embodiment, the microcontroller MC adapts the amplitude A of the search signal so as to maintain the magnitude of the clamp current near a predetermined value, thereby improving the measurement accuracy. Making the magnitude of the current constant corresponds to making the accumulated charge (integrated value of the displacement current) constant even if the capacitance of the capacitor changes. Specifically, when the amplitude of the clamp current is small, the amplitude of the search signal Vp as the common potential for equipotential driving is increased, and when the amplitude of the clamp current is large, the amplitude of the search signal Vp is decreased. Controlled by MC.

More preferably, the capacitance can be obtained from the amplitude A of the adaptive search signal Vp by feedback controlling the search signal voltage Vp so that the amplitude of the clamp current proportional to the amplitude coefficient A of the voltage is constant. This is to perform feedback control of the magnitude of the search signal Vp required to charge the virtual capacitor calibrated by the measurement target and the electrode with a predetermined charge, and is premised on the voltage clamp control of the electrode and the equipotential drive control. This is a charge clamp method unique to the present invention.

In the charge clamp method, when the amplitude of the search signal voltage Vp with respect to a known calibrated reference capacitance C0 is A0, when the amplitude of the adaptive search signal voltage Vp with respect to an arbitrary capacitance C is A, The relationship of C/C0=A/A0 is established. The information on the amplitude A can be directly obtained by rectifying and smoothing (integrating) the search signal Vp. Therefore, the capacitance C can be acquired only by measuring the amplitude A of the adaptive search signal voltage Vp by the feedback control.

In the present embodiment, the search signal Vp is a sine wave, but it is not limited to this and any waveform can be used. Also in this case, the capacitance can be obtained from the magnitude of the search signal voltage Vp when the capacitance C is charged with a predetermined charge.

The guard electrode and all electrodes are always driven at the same voltage as the search signal Vp by the configuration of the electrode section, voltage clamp control, equipotential drive control and charge clamp control in the probe according to the present invention. During the voltage clamp operation, the potential of the electrode detecting the clamp current is fixed to the search signal, so that highly stable and highly accurate gap measurement is possible. Further, it is possible to simultaneously obtain the clamp currents of a plurality of electrodes by installing a plurality of differential amplifiers INA.

<Gap measurement>
A gap measuring method using the gap sensor of the present invention will be described below.

Each electrode pair Ei forming the electrode pair array 4 in the probe 2 is arranged at the same position on the front surface P1 and the back surface P2 of the substrate 5 and independently connected to the control unit 10 incorporated in the main body 21 via the signal line Es. It

As shown in FIG. 5A, the probe 2 is inserted into the clearance G, and the capacitance at each position is detected by each electrode pair, and the capacitance between the upper electrode E1 and the surface S1 is To be acquired. Subsequently, the capacitance between the lower electrode E2 at the same position as the upper electrode E1 and the surface S2 is acquired. If the distance d1 between the upper electrode E1 and the surface S1 and the distance d2 between the lower electrode E2 and the surface S2 can be acquired from these capacitance data, the gap d between the facing surfaces S1 and S2 can be obtained. Can be asked. The two-dimensional distribution of the gap d around the electrode portion can be obtained by sequentially performing the same measurement for all the electrode pairs. The clearance data acquired by the clearance sensor 1 is transmitted to the controller 30 such as a tablet PC via the communication means 31 and processed there.

The electrode pairs 4 are discretely arranged on the probe 2, but have a plurality of electrode pairs, so that data at any position between neighboring electrode pairs can be calculated based on the position of the electrode pair and the gap data. That is, by supplementing the gap data of the three adjacent electrode pairs 4, the gap data at any position in the area surrounded by the electrode group can be calculated. Therefore, the gap sensor can be downsized according to the present embodiment, and a wide gap space can be continuously measured and displayed in 3D. Since the probe 2 is provided with the scale 28 in the main axis Xc direction, the position (depth) r of the measurement electrode Ei can be easily confirmed.

It is assumed that the member to be measured in the gap measurement is made of a conductive material such as aluminum alloy or carbon fiber, but even if it is a non-conductive material, the conductive material is coated along the surface at or near the surface. Alternatively, if it is covered, the gap can be measured.

In the gap measurement, the electrode surface is preferably parallel to the measurement surfaces S1 and S2, and the probe 2 may be attached to the measurement surface S1 by using the magnet 25 as shown in FIG. 6A. Since the magnetic filler film is formed on the surface of the probe 2, a more stable gap measurement can be performed by installing the magnet 25 so that the probe 2 is attracted to the measurement surface S1 side.

According to the present invention, it is possible to measure the gap accurately and with good reproducibility by adopting the unique electrode structure and using the equipotential driving method and the charge clamp control for the capacitance measurement. Since the equipotential driving method according to the present invention is a method in which the exploration signal has a common potential, it is possible to drive a plurality of electrodes and a plurality of guard patterns without using the three-layer substrate structure as in the present embodiment. The same effect can be obtained.

When performing the gap measurement, the gap sensor 1 is calibrated. A standard sample made of an aluminum plate and having a predetermined gap d0 is used for the calibration. The gap is, for example, 0.5 mm, 1 mm, 2 mm, 3 mm. The metal flat plate is grounded in common with the gap sensor 1. The probe 2 is inserted into the gap G of the reference sample, and the gap d0 is measured and calibrated. In the calibration, the reference amplitude A0 is corrected.

<Other Embodiments>
7 and 8 show another embodiment of the probe 2. The structure of the electrode portion is the same as that of the probe 2 of the embodiment of FIG. 2, but the electrode pairs 4a to 4e are arranged in two rows in a staggered arrangement along the main axis Xc of the probe 2 and are provided with 16-pole circular electrodes. The probe 2 is fixed to the main body 21 via a probe support portion (including a connector) 20 having a rotation shaft rotatable about the Y-axis direction. When the member such as the work on the upper side is a plate member, the main body 21 is installed on the upper surface of the plate member and the probe 2 is inserted into the gap G in a state of being folded on the bottom surface 21B. The probe support portion 20 is vertically movable according to the thickness of the plate member. Further, as shown in FIG. 6B, since the magnet 25 is built in the bottom of the main body 21, the magnetism of the filler film of the probe 2 can be used to attract the probe 2 to the surface S1.

As described above, the gap measurement adopts the charge clamp control in which the guard potential and the potentials of all the electrodes are made the same on the basis of the search signal Vp and the capacitances at the upper and lower electrodes of the electrode pair 4 are measured. Acquire the gap d data. The gap measurement is sequentially performed for all the electrode pairs 4.

A rotary encoder 23 as a position detecting sensor for measuring a moving distance (relative position) in the Y direction and a reference position detecting sensor 24 for confirming a reference position in the Y direction are arranged on the bottom surface 21B of the main body. Bar code-shaped markers detected by the reference position sensor 24 are arranged on the upper surface of the plate member at equal intervals in the Y direction, and the reference position detection sensor 24 reads the reflected light from the marker to detect the reference position. In the present embodiment, the probe 2 is rotated so as to be parallel to the bottom surface 21B of the main body 21, but the probe 2 is rotated so as to be parallel to the Z axis direction with respect to the gap extending in the YZ plane direction, for example. If this is done, gap measurement is possible.

Since the probe according to the present invention has a three-layer structure and the guards of the respective electrodes are commonly used, the probe can be made thin and a narrower gap can be measured. Further, since the guard potential is shared, the number of wirings can be reduced and many electrodes can be arranged on the probe. Further, by applying the equipotential drive control, all the electrodes and the guard potential are driven to the equipotential, which enables stable and highly reproducible measurement. Furthermore, by adopting the charge clamp method, the capacitance can be measured from the magnitude of the search signal.

1 Gap sensor 2 Probe 3 Electrode part, Xc Electrode part spindle 4 Electrode pair array 5 Multilayer substrate (flexible substrate)
C1 to C3 conductor pattern layer (wiring layer)
G1, G2, Ge Guard pattern E1, E2 Electrode Gb1, Gb2, Eb1, Eb2 Via hole S1, S2 Plate member (workpiece) surface G Gap 10 Control unit SG Signal generator, AMP Guard drive amplifier VCA1, VCA2, VCAn Voltage clamp amplifier INA differential amplifier (instrumentation amplifier)
SW1, SW2 selection switch MC Micro controller 20 Probe support (connector)
21 Main unit/measurement trolley (amplifier, communication)
21B Truck bottom (Magnetic suction part)
23 Position detection sensor (rotary encoder)
24 Reference position detection sensor 25 Magnetic attraction unit (magnet)
28 Scale 30 controller (tablet PC)
31 Communication means (wired, wireless)

Claims (10)

A gap sensor for detecting a gap between a surface of a first member having conductivity and a surface of a second member having conductivity, which face each other, by a capacitance measuring method,
A probe and a body extending along the main axis,
The probe is provided with a plurality of electrodes on the tip side, the base end of which is connected to the main body,
The probe has a multilayer substrate structure in which a first conductive layer, a second conductive layer, and a third conductive layer are stacked,
The first conductive layer defines a first surface of the probe, a first electrode group is formed in an array, a first guard layer electrically disconnected from the first electrode group is formed,
The third conductive layer defines the second surface of the probe, is formed by arranging the second electrode group at a position corresponding to the first electrode group, and is electrically disconnected from the second electrode group. 2 guard layers are formed,
The second conductive layer is disposed between the first conductive layer and the third conductive layer, a guard electrode is formed at a position corresponding to the first electrode group and the second electrode group, and is electrically non-contact with the guard electrode. A connected signal pattern is formed, and the signal pattern is electrically connected to each electrode of the first electrode group and the second electrode group,
The control unit of the main body is
Applying a search signal to the first guard layer, the guard electrode, and the second guard layer,
Voltage clamping each electrode of the first electrode group and the second electrode group with the search signal via the signal pattern,
A gap sensor characterized by measuring a gap at each electrode position by detecting a clamp current by a voltage clamp. The control unit is
An exploration signal generator,
A drive circuit that applies a voltage of a search signal to the first guard layer, the guard electrode, and the second guard layer;
A voltage clamp circuit that independently drives each electrode of the first electrode group and the second electrode group to clamp the voltage of the search signal;
A current detection circuit for detecting the clamp current of each electrode,
The gap sensor according to claim 1, wherein the gap is measured by calculating an electric capacity from the detected current. The voltage clamp circuit feeds back the error between the search signal and the voltage of each electrode to perform clamp control,
The gap sensor according to claim 1, wherein a current supplied via a clamp current detection resistor connected between the drive output of the voltage clamp circuit and each electrode is detected as a clamp current. The voltage clamp circuit is
A clamp current detection resistor is connected between the drive output of the clamp amplifier for performing voltage clamp control based on the search signal and the negative feedback input, and one end of the clamp current detection resistor on the negative feedback input side is connected to each electrode,
A reference current detection resistor is connected between the drive output and the negative feedback input of the reference clamp amplifier that controls the voltage clamp based on the search signal without being connected to the electrodes.
The gap sensor according to claim 2, wherein the current detection circuit includes a differential amplifier that calculates a difference between the drive output of the clamp amplifier and the drive output of the reference clamp amplifier. The feedback control of the magnitude of the search signal is performed so that the magnitude of the detected clamp current is constant, and the capacitance is calculated from the magnitude of the search signal. The gap sensor according to claim 1. The gap sensor according to claim 4, wherein the clamp amplifier and the reference clamp amplifier associated with each electrode of the first electrode group and the second electrode group are housed in one package. A gap measuring method for detecting a gap between a surface of a first member having conductivity and a surface of a second member having conductivity, which face each other by a capacitance measuring method. A plurality of electrode pairs and a guard layer are formed,
Generating an exploration signal,
Applying the probe signal to the guard layer;
Independently voltage-clamping each electrode of the plurality of electrode pairs to the probe signal;
Detecting the capacitance at each electrode position by measuring the clamp current of each electrode,
A gap measuring method comprising: measuring a gap at each electrode position based on the capacitance. The gap measuring method according to claim 7, wherein the search signal is a sine wave, and the amplitude of the sine wave is varied according to the magnitude of the clamp current. The amplitude of the search signal is feedback-controlled so that the magnitude of the clamp current is constant, and the capacitance is obtained from the amplitude of the search signal when the feedback control is performed. Gap measurement method. The gap measuring method according to claim 8 or 9, wherein a gap at an arbitrary position between the electrodes is complemented based on a gap distance between adjacent electrode pairs and a distance between the electrodes.

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